What is an Organ?
The organ as we know it developed from a group of individual organs brought together
into one place to be played by one person. Each of these organs as its own character
and volume controlled from its own keyboard. This allows for the use of contrasting
sounds; they can also be joined together to give a bigger sound. The sound is produced
by wind/air being blown into a pipe. They come in two (2) main types: flue and reeds.
Flue
These come in three (3) groups: foundation, flutes and strings.
Foundation
The main sound on the organ and does not resemble any other musical instrument.
Flutes
Pure, clear toned, a sound close to the flutes of the orchestra or the recorder etc.
Used in contrast to the foundations or for solos.
Strings
Luscious, sensual, bright and warm sound can be made imitate orchestral string
Reeds
Sound made by vibrating metal reed, can be a quiet stop (oboe) up to very-very loud
(Fanfare Trompette) for solos or made to blend with the foundations (Cornopean)
Tracker (or mechanical) action
The original and still the best method of connecting the movement of the fingers to the admission of air to the organ pipes. This was the only action up to the late 19th C and as had a geat revival in the last 30-40 years. This action has a great response and 'feel', the point at which the pallet opens can be felt and some organists are able to control the speed that the pallet opens.
The Action (fig 1)
Pressing the key down (A) this pivots about (B) the back of the key (C) pushes the sticker up. The pallet(G) is opened by
being pulled down by the tracker. Converting the up motion of the sticker to the downward motion of the tracker is achieved by the backfall which pivots about (E), up at (D)-down at (F). The problem 'tracker' had was that at the end of the 19th c organs got larger, increased number of manuals to be coupled together, and higher wind pressures(from 3"-4" up to 10"-12" for some reeds) the keys became unbearably heave to play prompting the development of other types of action. With modern materials and engineering 'know how' plus the influence of the authentic music movement tracker has, where possible become the action of choice.
Pneumatic (Supply, Pressure or Charge)
The action is shown in the ‘off’ position. The windchest [A],the power pneumatic motor(B) and key valve-chest [C] are filled with air under pressure. The key valve-chest [C] is connected to the primary Pneumatic motor (D) by pneumatic tubing (E). The pneumatic motor (D) is in a position of collapse because the lower end of the tubing is open to outer atmosphere through the valve (F). Depression of the key (G) moves the valve upwards so that the pneumatic tubing is at once sealed to the atmosphere and opened to the air pressure in the key valve (E) Which then travels up the tubing and inflates the primary motor (D). This in turn moves the valve (H)
so that the supply of pressurised air is cut of from the power motor (B), simultaneously the air within it is exhausted into the outside atmosphere. The power motor (B) then collapses under the air pressure in the windchest [A] pulling open the main pallet (J) against the tension of its spring (K) and admitting the wind to the pipes. Release of the key returns the valve (F) to the ‘off’ position,opening the tubing to the outer atmosphere, and the train of events is reversed.
